Description

Given an array nums, write a function to move all 0's to the end of it while maintaining the relative order of the non-zero elements.

For example, given nums = [0, 1, 0, 3, 12], after calling your function, nums should be [1, 3, 12, 0, 0].

Note:
You must do this in-place without making a copy of the array.
Minimize the total number of operations.

Solution

Two-pointers

class Solution {
    public void moveZeroes(int[] nums) {
        if (nums == null || nums.length == 0) {
            return;
        }
        
        int j = 0;
        for (int i = 0; i < nums.length; ++i) {
            if (nums[i] != 0) {
                swap(nums, i, j++);
            }
        }
    }
    
    private void swap(int[] nums, int i, int j) {
        if (i == j) {
            return;
        }
        
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}